1. Field of the Invention
The present invention relates to a noise damping device of a rotation driving apparatus, which can dampen noise caused by air flow generated when disks such as hard disks installed within a housing are rotated.
2. Description of the Related Art
As an example of a rotation driving apparatus, a hard disk drive (HDD) shown in FIG. 1 comprises a housing including a base frame 12 installed in a computer main body (not shown) for supporting hard disks 18 and a cover frame 14 assembled to the base frame 12 for protecting the hard disks 18, and a noise damping device.
The hard disks 18 are rotated by a driving source such as a spindle motor (not shown) installed on the base frame 12 so that a predetermined data recording/reproducing means (not shown) can record data on the hard disks 18 or reproduce the data recorded on the hard disks 18.
The noise damping device is attached to the outer surface of the cover frame 14 by an adhesive such as a bond or a double-sided bonding tape so that the noise damping device can absorb noise generated within the housing 10, and comprises a damper member 16 usually manufactured of stainless steel in a thin plate structure.
In the above structure, when the hard disks 18 are rotated at high speed so as to record data on the hard disks 18 or reproduce the recorded data, noise is generated within the housing 10.
The noise can be classified into, for example, a structure-borne sound such as a solid-borne sound generated when impact and vibrations which a structural body experiences from a driving source propagate through the structural body, and a pneumatic or flow sound such as an air-borne sound generated when a structural body is forcibly vibrated by air flow. The air-borne sound is generated by an irregular eddy flow between a first boundary layer 22 and a second boundary layer 24 wherein the first boundary layer 22 flows in a direction away from a rotation center D between the hard disks 18 and the cover frame 14, and the second boundary layer 24 flows from outer sides to the rotation center D as shown in FIG. 2.
The noise generated in the housing 10 can be absorbed and reduced, to a certain extent, by the damper member 16. However, in the above conventional art, since the damper member 16 for damping noise must be separately attached to the outer surface of the housing 10, the manufacturing cost is high and more assembly operations are required. In addition, when the temperature within the computer main body rises, the bonding force of the adhesive deteriorates due to heat generated in the computer main body.
To solve the above problems, it is an objective of the present invention to provide a noise damping device of a rotation driving apparatus, the structure of which is improved so that noises can be dampened by fundamentally suppressing abnormal air flow generated when disks rotate within a housing.
Accordingly, to achieve the above objective, there is provided a noise damping device of a rotation driving apparatus comprising: a housing; and at least one rotating disk installed to be rotated by a driving source within the housing, wherein the rotating disk and the housing are assembled to satisfy the following Equation,
xcex4m less than h less than xcex4m+1.5xcex4f
where xcex4m is the thickness of air layers which move from a rotation center of the rotating disk to the outside thereof and are distributed around the rotating disk when the rotating disk rotates at a normal operating speed, xcex4f is the thickness of air layers which move from the outside of the rotating disk to the rotation center thereof and are distributed around an upper inside surface and the base surface of a housing, which face the rotating disk, and h is the distance between the rotating disk and the upper inside surface or the base surface of the housing.
In addition, it is preferable that the housing includes a base frame for supporting the rotating disk, and a cover frame assembled to the base frame to cover the rotating disk. The cover frame is installed on the base frame so that the following Equation can be satisfied,
xe2x80x83xcex4m less than h1 less than xcex4m+1.5xcex4f
where h1 is the distance between the rotating disk and the cover frame.
Additionally, it is preferable that the rotating disk is installed on the base frame so that the following Equation can be satisfied,
xcex4m less than h2 less than xcex4m+1.5xcex4f
where h2 is the distance between the rotating disk and the base frame.